Method of making shell molds for casting reactive metals



United States Patent 3,321,005 METHOD OF MAKEN G SHELL MOLDS FOR CASTlNGREACTIVE METALS Nick G. Lirones, North Muskegon, Mich., assignor toHowrnet Corporation, a corporation of Delaware No Drawing. Filed Apr.19, 1965, Ser. No. 449,294 20 Claims. (Cl. 164-26) This inventionrelates to the preparation of molds in which shaped products may be castof metals such as beryllium, titanium, zirconium, hafnium, molybdenum,tungsten, uranium, and the like refractory metals, reactive heavy metalsand metals of group IV-b of the periodic system.

The invention will be described with reference to the preparation anduse of a mold formed about a heat or otherwise disposable pattern byrepeatedly wetting with a dip coat composition and stuccoing to build upa monolithic structure from which the pattern is removed to leave acorresponding mold cavity into which molten metal may be directly castto produce a metal product having a shape corresponding to the cavityleft by the removed pattern. It will be understood that the concepts ofthis invention Will have application also to the mold that is formed byinvestment of the monolithic structure in a ceramic body for support, inaccordance with conventional investment casting procedures, but it ispreferred to make use of the monolithic structure without investmentwhen suflicient strength can be embodied in the walls of the monolithicstructure to enable the molten metal to be poured directly thereinwithout support.

As described in the patents of Collins No. 2,380,945; Feagin et al. No.2,439,207, No. 2,441,695 and No. 2,521,839, and Operhall et al. No.2,961,751, such monolithic mold structures are produced by immersion ofa cluster of wax patterns into a dip coat composition formulated of aninorganic binder, such as colloidal silica, and a ceramic flour such asis formed of silica, zircon, alumina, fused quartz and the like. Whilethe pattern is wet with the dip coat composition, application is made ofa stucco, such as larger particles of silica, zircon, alundum, fusedquartz and the like ceramic materials, by sprinkling the stucco onto thepattern wet with the dip coat composition whereby a layer of the stuccois retained on the wet surface. This procedure of wetting with the dipcoat composition and stuccoing is repeated for a number of times withintermediate drying until a composite layer of the desired thickness andstrength has been built up about the cluster formed of a number of thepatterns of wax or other preferably heat disposable material.

Thereafter, the assembly is heated to a temperature above the meltingpoint temperature of the wax to remove the pattern and the remainingmold, having a mold cavity corresponding in shape to the displacedpattern, is fired at an elevated temperature in the range of l5002300'F. to cure the mold.

While molds of the type described are suitable for use in casting shapedproducts of steels and alloys of steels including steels alloyed withnickel, cobalt and the like, they have been found to be unsuitable foruse in the casting of shaped products from such high melting pointmetals as the refractory metals or reactive heavy metals such astitanium, zirconium, uranium, hafnium, beryllium, or other metals of thegroup IV-b series. One of the major difficulties stems from thereactions that take place at the elevated temperature of the moltenmetal between the molten metals and the silicon oxides or ceramiccomponents making up the mold. This results not only in an imperfectcasting or a casting in which the reaction which takes place at thesurface produces an imperfect casting but the reactions taking placeoperate also to ice modify the chemistry of the cast product and toproduce an unsound casting.

In the copending application Ser. No. 407,256, filed Oct. 28, 1964,description is made of a procedure for protection of the ceramicmaterials in the mold for the purpose of minimizing reaction with themolten metals. For this purpose, colloidal graphite is incorporated as acomponent in the dip coat composition to coat the individual ceramicparticles with the non-reactive colloidal graphite. While someimprovement is derived from the described combination of colloidalgraphite with the ceramic particles of the dip coat composition, acontinuous protective surface is not made available whereby undesirablereactions are still capable of taking place.

It is an object of this invention to produce and to provide a method forproducing ceramic molds of the type described wherein the formed moldcan successfully be employed for the casting of metals and alloys of thetypes heretofore described including beryllium, titanium, zirconium,hafnium, molybdenum, tungsten, uranium, and the like refractory metals,heavy reactive metals and metals of group IV-b of the periodic system.It is a related object to provide a method for the casting of shapedproducts of such metals in molds of the type described.

It has been found that a mold formed of ceramic material of the typesdescribed can be used in the production of shaped products of metals ofthe types described and alloys thereof when the individual particles ofthe ceramic materials making up the mold portion immediately surroundingthe mold cavity, and preferably the entire crosssection of the moldwalls, are provided with a substantially continuous coating of an inertcarbonaceous material formed in situ in the mold by thermaldecomposition of an organic material and preferably by thermaldecomposition of an organic resinous material such as a phenol aldehyderesin, cresol aldehyde resin, furfural aldehyde resin, resorcinolaldehyde resin, acrylic acid ester polymer, and the like.

In practice, the thermally reducible organic resinous material can beincorporated into the mold by formulation of the resinous material as apart of the dip coat composition whereby such organic resinous componentwill become uniformly distributed substantially throughout thecross-section of the mold wall that is formed about the disposablepattern. Instead, the organic resinous component can be introduced intothe mold Walls after removal of the disposable pattern by impregnationof the resulting mold with a dilute solution or dispersion of theorganic resinous component in a suitable solvent or aqueous medium. Whenincorporated by impregnation of the mold, it is preferred to effect suchimpregnation from the inside out by introducing the impregnatingcomposition into the formed mold cavity so that the maximum amount ofimpregnation will be achieved in the portions of the mold wallimmediately surrounding the mold cavity. It will be understood that acombination including the formulation of the clip coat composition tocontain the heat decomposable organic resinous component plusimpregnation of the formed mold with a solution or dispersion of anorganic resinous component can be employed for more effective andefiicient coverage of the ceramic materials making up the mold.

When the mold is thereafter hated to cure the mold or to fire the mold,if such heating is effected while the mold is in a non oxidizing orinert atmosphere, then instead of burning out the organic resinouscomponent, the resinous component will thermally break down to atenacious carbonaceous residue of an inert form of carbon orcarbonaceous material which will effectively coat the inorganic orceramic particles in at least the portions of the mold adjacent the moldcavity. This will result in a substantially continuous covering whichwill protect the ceramic or inorganic materials to enable the describedmolten metals or alloys to be poured directly into the mold cavitywithout reaction with components making up the mold.

When the organic resinous component is incorporated to form a part ofthe dip coat composition, the organic resinous component can be embodiedin the dip coat composition in addition to the conventional ceramicbinder, such as colloidal silica. Instead, the inorganic bindercomponent can be eliminated whereby the organic resinous material willfunction in the dip coat composition as an interim binder for thebuildup of the layers of ceramic flour and stucco. When formulated incombination with a conventional binder, the dip coat composition can beformulated to contain the organic resinous component in an amount withinthe range of 40% by weight and preferably in an amount within the rangeof 25% by weight. When formulated into the dip coat composition withouta conventional ceramic binder, the amount of organic resinous componentis preferably increased to within the range of 10-40% by weight andpreferably an amount within the range of -30% by weight of the dip coatcomposition.

It is preferred to incorporate the organic resinous component in adissolved state so as to form a coating about the ceramic particles upondrying. For such purpose, use can be made of a diluent in the form of aconventional aqueous medium when the resinous component is in a watersoluble or A stage. In the event that the organic resinous component iswater insoluble, the dip coat composition can be formulated with anorganic solvent in which the resinous material is soluble or the organicresinous component can be incorporated as a dispersed phase in theaqueous medium to enable formulation of the dip coat composition as anaqueous system.

When the organic resinous material is incorporated by way ofimpregnation of an already formed mold, it is desirable to make use ofthe organic resinous material in a dilute solution in an organic solventor a dilute dispersion in an aqueous medium. The amount of the organicresinous component formulated into the impregnating composition willdepend somewhat on the character and the molecular weight of theresinous system. As a general rule, a satisfactory impregnatingcomposition can be formulated with the organic resinous componentpresent in an amount within the range of 1-80% by weight and preferably2-10% by weight. It will be understood that when a larger amount ofresinous material is required in the formed mold, the impregnationprocess can be repeated one or more times.

The process of impregnation is often preferred as the means for theincorporation of the organic resinous component since such impregnationwill operate not only to coat the ceramic flour of the dip coatcomposition but also the stucco which has been ap lied. Equivalentresults can be achieved by the formulation of the dip coat compositionto contain the organic resinous material, as previously described, andwherein the stucco has been precoated with an organic resinous material,as by wash coating with a solution thereof and which will hereinafter bereferred to as resinous precoated ceramic stucco.

Having described the basic concepts of this invention, illustration willbe made first of the system wherein the organic resinous material isincorporated to form a component of the dip coat composition.

A cluster of wax patterns is formed in the conventional manner byattachment of the patterns to runners, also formed of wax or other heatdisposable materials, and to a funnel or cup which communicates with therunners to define the opening in the mold through which the molten metalis poured for filling the mold cavity. Instead of wax, the patterns,runners and/or funnel can be formed or plastic or other heat disposablematerials, or of materials which can be disposed of by chemicalsolution, sublimation or by mere increase to room temperature, as in thefrozen mercury process.

The cluster should be inspected for the removal of dirt, flakes or othermaterials which might have adhered to the surfaces of the patterns andwhich, if allowed to remain, would reproduce and provide imperfectionsin the surfaces of the metal casting.

Example 1 Dip coat composition (with ceramic binder): Colloidal silica(30% grade, 1.198 specific gravity) cc 8000 Zircon (99% through 325mesh) pounds 165 Water cc 6150 Water soluble A-stage phenol aldehyderesin pounds 30 Sodium fluoride grams 110 Example 2 Dip coat composition(without ceramic binder):

Percent by wt. Liquid phenol formaldehyde resin (Catalin 136) 27Isopropyl alcohol 35 Silica flour (-325 mesh) 38 The cleaned cluster isimmersed in the slurry c0mpris ing the dip coat composition to wet allof the surfaces with the exception of the lip of the pouring spout.Instead of dipping, the surfaces can be wet with the slurry of the dipcoat composition by other coating techniques, such as by flow coating,spray coating and the like.

While the cluster is still wet with the dip coat composition, a finelydivided, dry stucco is sprinkled over the surfaces whereby some of thestucco will adhere to the wet coating of the dip coat composition and beretained on the surfaces of the pattern for integration with the slurryof the dip coat composition to form a composite layer therewith aboutthe cluster. The stucco can also be applied onto the wet surfaces of thecluster by means of a moving bed into which the cluster is immersedsubstantially completely to coat the wet surfaces of the cluster withthe stucco material. As the stucco, use can be made of alumina, zircon,silicate, fused silica, with or without resinous pretreatment, and inwhich the stucco is dimensioned, at least in the first few coats, to beless than 50 mesh but more than mesh. The cycle of wetting with the dipcoat composition and stuccoing is repeated a number of times, withintermediate drying between each cycle, until -a composite layer of thedesired thickness has been built up about the walls of the clusterincluding the patterns and parts. A mold having a wall thickness builtup to about A to /2 inch usually provides strength suflicient forinvestment or to enable the molten metal to be poured directly into themold for the production of shaped metal products of normal weight. Thebuildup of walls of greater thickness can be produced for use in themolding of larger and heavy castings. Usually, a wall thickness of A to/2 inch can be achieved with from five to ten cycles of dip coating,stuccoing, and intermediate drying.

While it is preferred to make use of dip coat compositions of the sameformulation for all cycles thereby uniformly to distribute the organicresinous material throughout the cross-section of the mold wall, it willbe sufficient if only the inner one-half of the wall cross section isformed of the dip coat composition containing the organic resinouscomponent while the remainder of the built-up wall is formed of aconventional dip coat composition formulated with ceramic materials.

'After drying, the composite structure is dewaxed by inverting the moldand by heating to a temperature above the melting point temperature forthe wax and preferably to a temperature above 400 F. but below thetemperature at which the organic resinous material will be burned out ofthe mold. Dewaxing can be carried out by other processes such as hotsand dewaxing wherein the mold is surrounded with sand preheated to atemperature within the range of 400-800 F. or in which the hot sand ispoured over the mold; steam dewaxing wherein the composite structure ishoused in an autoclave or else steam at high pressure is introduced ontothe mold.

The dewaxing step can be carried out as a separate operation in themanner described but it is preferred to combine the dewaxing step withthe subsequent step of curing the mold wherein the mold, with the waxpattern or after the wax pattern has been removed by one or the other ofthe dewaxing processes, is introduced into a zone heated to atemperature above 800 F. and preferably to a temperature within therange of 1000- 2300 F. while the atmosphere in the zone is maintained asan inert or non-oxidizing or reducing atmosphere, as by the use of aninert gas such as argon, nitrogen, carbon dioxide and the like. Undersuch conditions, the mold is cured and the organic resinous component isthermally decomposed to a stable form of carbon or carbonaceousdecomposition product which effectively coats the adjacent ceramicmaterials with a protective coating that blocks reaction between theceramic and hot molten metals poured into the cavity of the mold. Thedesired cure and thermal breakdown of the organic resinous material canusually be achieved at the there is no harm in heating for a longerperiod of time to insure complete stabilization of the materials makingup the mold.

It has been found that the carbonaceous decomposition product that isformed is of the type which either swells or otherwise operates to fillup interstices of the mold since the formed mold is less pervious to thepenetration of the molten metal poured into the mold cavity while stillproviding microporous openings through which the mold can breathethereby to block reaction between .the metal and the materials of themold while at the same time providing a more uniform smooth surface atthe interface for the production of a molded product which conforms moreexactly with the original shape of the mold cavity and with less surfaceimperfection. Thus there is produced an acceptable product of suchmetals which have heretofore been incapable of being processed inceramic molds.

Description will now be made of the alternative process wherein theorganic resinous material is incorporated after the ceramic mold hasbeen formed and dewaxed. For this purpose, the conventional processeswhich make use of conventional ceramic materials as described in theaforementioned patents can be used up to the point that the formedceramic mold is dewaxed or dewaxed and cured.

Thereafter, in accordance with the concepts of this invention, asolution of .5% to 25% by weight furfural formaldehyde resin or asolution of .5% to 80% by Weight of a phenol or cresol formaldehyderesin in propanol is poured into the mold cavity for flow as byimpregnation into the interstices of the porous mold. The step ofimpregnation can be repeated one or more times if a higher concentrationof the organic resinous component is desired in the mold walls. Usuallythe step of pour ing the impregnating composition into the mold isfollowed by removal of the material that remains and by drying beforesubsequent re-introduction of impregnating composition for increasingthe amount of material introduced into the mold walls. The driedresinous material coats the ceramic flour and stucco making up the adjacent portions of the mold walls.

Thereafter, the mold is fired in the manner previously described forcuring in an inert or non-oxidizing atmosphere to effect the thermaldecomposition of the impregnating organic resinous material forreduction thereof to temperature described in from 15 to minutes but theinert carbonaceous decomposition product coating the ceramic particlesof the mold and filling the interstices of the mold to block penetrationof molten metal poured into the mold cavity during the subsequent. stepsof metal casting.

It will be understood that both of the prevously de scribed systems maybe combined to produce a mold having the organic resinous componentincorporated into the walls of the mold by way of a dip coat compositionand in which additional organic resinous material is incorporated, atleast in the inner portions of the mold about the mold cavity, by thesubsequent process of impregnation.

It is believed that the stabilized thermal decomposition product formedof the organic resinous component is capable also of the characteristicsof a binder in the cured product since a mold of the desired strengthresults even though no ceramic binder is present in the dip coatcomposition.

Although not equivalent to the described easily thermally decomposableorganic resinous material in the described formulations, other organicmaterials which are easily thermally decomposable to a stabilized carbonor carbonaceous reaction product can be employed as the organiccomponent in the amounts described for the organic resinous material inthe preceding examples. Such other materials which can be substitutedfor the organic resinous materials in equivalent amounts in theforegoing examples include natural resins and gums, such as copal resin,ester gum, gum tragacanth, gum arabic, terpene resins, coumarone indeneresins and the like; sugars, carbohydrates and starches such as casein,albumen, algins and the like; coal tar and petroleum resins and thelike.

Molten metal can be poured directly :into the mold cavity for thefabrication of molded products since the mold possesses sufiicientstrength and has sufficient mass integrity to enable the motlen metal tobe poured directly into the mold. While preheating is not essential, itis desirable to preheat the mold prior to metal pouring. If thegraphitized mold is to be preheated to a temperature above 800 F, it isdesirable either to effect such preheat under vacuum conditions or in aninert or non-oxidizing atmosphere, as in an atmosphere of argon,nitrogen or carbon monoxide or carbon dioxide, otherwise thecarbonaceous product will burn from the mold. Since the describedrefractory metals, reactive heavy metals or metals of the group IV-bhave a melting point far in excess of 800 B, it is desirable to achievemetal pouring by vacuum casting techniques wherein the mold is enclosedwithin a vacuum chamber which communicates with a melting furnacewhereby a vacuum can be drawn to evacuate the chamber and the mold priorto metal poun'ng. The mold and metal cast therein are preferablymaintained under vacuum conditions until the poured metal has solidifiedor cooled to a temperature below 800 F. Thereafter, the assembly can beremoved from the vacuum chamber for further processing.

To assist in filling the mold, centrifugal casting techniques can beemployed in combination with metal pouring. By way of specificillustration, description will be made of the use of a mold embodyingthe features of this invention in the preparation of a cast metalproduct of titanium, it being understood that others of the heretoforedescribed refractory metals, heavy reactive metals or metals of grouplV-b and alloys thereof may be similarly processed.

In practice, the mold is housed in a vacuum chamber on the underside ofa melting furnace and the molten titanium is poured under vacuum intothe mold, with or without preheating the mold. When preheating isemployed, it is desirable to preheat the mold while under vacuumconditions in which the preheat may be to a temperature up to 800 F.although preheating to higher temperatures is preferred.

The poured metal is allowed to cool in the vacuum chamber or under aprotective inert or non-oxidizing atmosphere to a temperature below thatat which oxidation of the carbonaceous material can take place beforeremoval :of the cast metal product from the protective atmosphere of themold. The cast metal product can be removed by conventional techniquessuch as by impacting and shaking to disintegrate the mold and free thecasting.

It will be apparent from the foregoing that I have provided a new andnovel mold system which makes use of ceramic materials and in whichshaped products can be successfully produced of such metals as titanium,zirconium, uranium, hafnium, beryllium, or other metals of the groupIV-b of the period system.

As used herein, the terms ceramic flour and ceramic stucco are intendedto include flour and stucco formed of ceramic materials such as silica,fused glass, fused quartz, Zirconium silicates, ores such as beryl ores,thoria, zirconite, kyanite, mullite and sillamanite, and oxides of thetypes previously described including zircon and alumina.

It will be understood that changes may be made in the details offormulation, fabrication and construction of the mold without departingfrom the spirit of the invention, especially as defined in the followingclaims.

I claim:

1. In the method of producing a mold for use in casting shaped productsof refractory metals, heavy reactive metals, metals of group IV-b of theperiodic system and alloys thereof in which use is made of a disposablepattern of the shaped product, the steps of wetting the surfaces of thepattern with a fluid composition the solids of which consist essentiallyof the combination of a ceramic flour and an organic resinous materialwhich is easily thermally decomposable in a non-oxidizing atmosphere to:a stable form of a carbonaceous decomposition product, :applying aceramic stucco to the surfaces of the pattern while wet with the dipcoat composition whereby some of the stucco is retained on the Wetsurfaces, repeating the applications of dip coat composition and stuccofor a number of cycles to form a composite layer of the dip coat solidsand stucco on the surfaces of the pattern, treating the composite toeffect removal of the pattern and provide a mold having a mold cavitycorresponding to the removed pattern, heating the mold to a temperaturein excess of 800 F. in a non-oxidizing atmosphere to cure the mold andthermally decompose the organic binder component in situ in the mold toproduce a mold in which the ceramic particles in at least the wallportions about the mold cavity are protected by the carbonaceous thermaldecomposition product.

2. The method as claimed in claim 1 in which the organic resinous binderis selected from the group consisting of phenol aldehyde resin, cresolaldehyde resin, resorcinol aldehyde resin, and furfural aldehyde resin.

3. The method as claimed in claim 1 in which the organic resinouscomponent is present in the dip coat composition in an amount within therange of 540% by weight.

4. The method as claimed in claim 1 in which the stucco is precoatedwith an organic thermally decomposable material.

5. The method as claimed in claim 1 in which the composite is heated toa temperature within the range of 1000-2300 F. in the non-oxidizingatmosphere.

6. In the method of producing a mold for use in casting shaped productsof refractory metals, heavy reactive metals, metals of the group IVb ofthe periodic system and alloys thereof in which use is made of a heatdisposable pattern of the shaped product, the steps of wetting thesurfaces of the pattern with a fluid composition the solids of whichconsist essentially of the combination of a ceramic flour and an organicmaterial which is easily thermally decomposable in a non-oxidizingatmosphere to a stable form of carbon, applying a ceramic stucco to thesurfaces of the pattern while wet with the dip coat composition wherebysome of the stucco is retained on the wet surfaces, repeating theapplications of dip coat composition and stucco for a number of cycleswith intermittent drying whereby a composite layer of the dip coatsolids and stucco is built up on the surface of the pattern, heating thecomposite to a temperature above the melting point temperature of thematerial of which the pattern is formed to effect removal of the patternand heating the mold to a temperature in excess of 800 F. in anonoxidizing atmosphere to cure the mold and thermally decompose theorganic component in situ in the mold to produce a mold in which theceramic particles in at least the wall portions about the mold cavityare protected with the carbonaceous thermal decomposition product.

7. The method as claimed in claim 6 in which the organic component ofthe dip coat composition is selected from the group consisting of asynthetic resin, a natural resin, a gum, starch, a protein, and acarbohydrate.

8. In the method of producing a mold for use in casting shaped productsof refractory metals, heavy reactive metals, metals of group IV-b of theperiodic system, and alloys thereof in which use is made of a disposablepattern of the shaped product, the steps of wetting the surfaces of thepattern with a fluid composition the solids of which consist essentiallyof the combination of a ceramic tbinder, a ceramic flour and an organicresinous material which is easily thermally decomposable in anon-oxidizing atmosphere to a stable form of carbonaceous decompositionproduct, applying a ceramic stucco to the surfaces of the pattern whilewet 'with the dip coat composition whereby some of the stucco isretained on the wet surfaces, repeating the applications of dip coatcomposition and stucco for a number of cycles to form a composite layerof the dip coat solids and stucco on the surfaces of the pattern,treating the composite to effect removal of the pattern and provide amold having a mold cavity corresponding to the removed pattern, heatingthe mold to a temperature in excess of 800 F. in a non-oxidizingatmosphere to cure the mold and thermally decompose the organic bindercomponent in situ in the mold to produce a mold in which the ceramicparticles in at least the wall portions about the mold cavity areprotected by the carbonaceous thermal decomposition product.

9. The method as claimed in claim 8 in which the organic resinouscomponent is selected from the group consisting of a phenol aldehyderesin, a cresol aldehyde resin, a resorcinol aldehyde resin, and afurfural aldehyde resin.

10. The method as claimed in claim 8 in which the organic resinouscomponent is present in an amount within the range of 540'% by weight ofthe dip coat composition.

11. The method as claimed in claim 8 in which the mold is heated to atemperature within the range of 10002300 F. in a non-oxidizingatmosphere.

12. In the method of producing a mold for use in casting shaped productsof refractory metals, heavy reactive metals, metals of group IV-b of theperiodic system, and alloys thereof in which use is made of a heatdisposable pattern of the shaped product, the steps of wetting thesurfaces of the pattern with a fluid composition the solids of whichconsist essentially of the combination of a ceramic binder, a ceramicflour and an organic material which is easily thermally decomposable ina non-oxidizing atmosphere to a stable form of carbonaceousdecomposition pro-duct and which is present in the dip coat compositionin an amount within the range of 540% by weight, applying a ceramicstucco to the surfaces of the pattern while wet with the dip coatcomposition whereby some of the stucco is retained on the wet surfaces,repeating the applications of dip coat composition and stucco for anumber of cycles, with intermediate drying, whereby a composite layer ofthe dip coat solid and stucco is built up on the surfaces of thepattern, heating the composite to a temperature above the temperaturefor disposal of the pattern whereby the pattern is removed from themold, heating the mold to a temperature within the range of l0002300 F.in a nonoxidizing atmosphere to cure the mold and thermally decomposethe organic component in situ in the mold to produce a mold in which theceramic particles in at least the wall portions about the mold cavityare provided with a protective coating of the carbonaceous thermaldecomposition product.

13. In the method of producing a mold for use in casting shaped productsof refractory metals, heavy reactive metals, metals of group IV-b of theperiodic system, and alloys thereof in which the mold is formed of acomposite of a dip coat composition the solids of which consistessentially of a ceramic flour and a ceramic binder and a stucco ofceramic particles, the steps of impregnating the mold with a dilutefluid composition containing an organic compound which is easilythermally decomposable to a stable carbonaceous decomposition product,firing the impregnated mold in a non-oxidizing atmosphere to atemperature above the thermal decomposition temperature for the organicmaterial thermally to decompose the organic material in situ in theimpregnated mold.

14. The method as claimed in claim 13 in which the step of impregnationis repeated a number of times with intermediate drying.

15. The method as claimed in claim 13 in which the impregnated mold isfired to a temperature Within the range of 1000-2300 F.

16. The method as claimed in claim 13 in which the organic material isan organic resinous polymer,

17. The method as claimed in claim 16 in which the organic resinouspolymer is selected from the group consisting of a phenol aldehyderesin, a cresol aldehyde resin,

a resorcinol aldehyde resin, and a furfural aldehyde resin.

18. The method as claimed in claim 1 which includes the step ofimpregnating the mold subsequent to pattern removal but prior to curingwith a fluid composition containing an organic compound which isthermally decomposab-le to a stable carbonaceous decomposition product.19. The method as claimed in claim 18 in which the organic material inthe impregnating composition comprises an organic resinous polymericmaterial.

20. The method as claimed in claim 8 which includes the step ofimpregnating the mold subsequent to pattern removal but prior to curingwith a fluid composition containing an organic resinous material.

References Cited by the Examiner UNITED STATES PATENTS 20 2,683,2967/1954 Drumm et al 22-193 2,886,869 5/1959 Webb et al. 22196 2,961,75111/1960 Operhall et al 22-193 2,991,267 7/1961 Bean 22-193 X 253,005,244 10/1961 Erdle et al. 22-196 3,042,541 7/1962 Kaplan 10638.22X

I. SPENCER OVERHOLSER, Primary Examiner,

E. MAR, Assistant Examiner, 3Q

13. IN THE METHOD OF PRODUCING A MOLD FOR USE IN CASTING SHAPED PRODUCTSOF REFRACTORY METALS, HEAVY REACTIVE METALS, METALS OF GROUP IV-B OF THEPERIODIC SYSTEM, AND ALLOYS THEREOF IN WHICH THE MOLD IS FORMED OF ACOMPOSITE OF A DIP COAT COMPOSITION THE SOLIDS OF WHICH CONSISTESSENTIALLY OF A CERAMIC FLOUR AND A CERAMIC BINDER AND A STUCCO OFCERAMIC PARTICLES, THE STEPS OF IMPREGNATING THE MOLD WITH A DILUTEFLUID COMPOSITION CONTAINING AN ORGANIC COMPOUND WHICH IS EASILYTHERMALLY DECOMPOSABLE TO A STABLE CARBONACEOUS DECOMPOSITION PRODUCT,FIRING THE IMPREGNATED MOLD IN A NON-OXIDIZING ATMOSPHERE TO ATEMPERATURE ABOVE THE THERMAL DECOMPOSITION TEMPERATURE FOR THE ORGANICMATERIAL THERMALLY TO DECOMPOSE THE ORGANIC MATERIAL IN SITU IN THEIMPREGNATED MOLD.